Electron waveguide devices are well known and are based on the propagation of the electron as described by its wave character and governed by the Schroedinger Equation. (For purposes of this description, the term, "electron waveguide," shall refer to mesoscopic semiconductor quantum structures the width of which being comparable to the electron wavelength.) They are similar in concept to microwave waveguides, but significantly different in application and detailed operation because standard classical transport theory, where self-averaging over many microscopic configurations is assumed, simply cannot describe these mesoscopic systems. One such difference is that undesirable electron waveguide modes can propagate through integrated circuits built with such electron waveguide elements. This leads to degradation in the operation of quantum interference devices used in such mesoscopic circuits as well as degradation in the propagation of the electron waves in interconnecting waveguide structures both of which are caused by the superposition of different longitudinal and lateral propagation modes.
The advantages of single mode propagation in electron waveguides (quantum wires) are discussed in GaAs and Related Compounds--1988, Inst. of Physics, Philadelphia, 1989 in an article by Sakaki.
The operation of many mesoscopic devices, for example, the quantum modulated transistor (QMT or the T-shaped electron waveguide transistor), the quantum wire transistor, and the Aharonhov-Bohm interferometer are all controlled by interference of the electron wave functions. The principles of T-shaped electron waveguide transistors and the Aharonhov-Bohm interferometers are described in the publication Nanostructure Physics and Fabrication, Academic Press, San Diego 1989 in articles by F. Sols et al, entitled, "Criteria For Transistor Action Based on Quantum Interference Phenomena," by D. C. Miller et al, entitled, "Modulation of the Conductance of T-Shaped Electron Waveguide Structures with a Remote Gate," and by S. Bandyopadhyay et al, entitled, "Quantum Devices Based on Phase Coherent Lateral Quantum Transport," respectively, all of which are incorporated herein by reference.
Optimum operation of these quantum interference devices requires a sharp interference pattern and requires that only one lateral waveguide mode be present (preferably the fundamental mode) and that the momentum k.sub.x in the direction of propagation be restricted to a narrow range of values. Therefore, propagation through an electron waveguide is most efficient at electron energies below the minimum required for scattering into higher lateral modes by elastic or phonon processes and below the minimum energy for significant inelastic scattering.